1. Field of the Invention
The present invention relates to an electronic part such as a laminated ceramic capacitor and a manufacturing method thereof.
2. Description of the Prior Art
A laminated ceramic capacitor, which is an example of laminated electronic part, is known as a chip-like electronic part. This laminated capacitor consists of a laminated body, which has a rectangular parallelepiped form and is composed of alternately laminated electrically conductive internal electrode layers and ceramic insulator layers, and external electrodes which are conductively connected to the internal electrodes and are formed at both ends of the laminated body.
For manufacturing this laminated ceramic capacitor, a method described below is known:
First, an electrically conductive paste, which forms the internal electrodes, is applied to ceramic green sheets composed of a dielectric ceramic material in a predetermined pattern. Ag, Pd, Agxe2x80x94Pd, Ni or Cu, for example, is used as the electrically conductive paste.
Then, a sheet laminated body is formed by stacking a plurality of the ceramic green sheets. Thereafter, this sheet laminated body as a whole is bonded under pressure. Further, a laminated chip, which has a rectangular parallelepiped form, is obtained by cutting the sheet laminated body in predetermined width and length. The sheet laminated body is cut so that the internal electrodes are exposed on cut surfaces.
Then, the laminated chip is heated to approximately 300xc2x0 C. in atmosphere for de-binding treatment, to vaporize an organic binder component contained on the laminated chip. Thereafter, a laminated body, which is made of a ceramic material, is obtained by firing the laminated chip at approximately 1300xc2x0 C. in atmosphere.
Finally, external electrodes, which are conductively connected to the internal electrodes, are formed at both the ends of the laminated body. The external electrodes are formed by a dry process, which is typically represented by the vacuum deposition and sputtering. Thin films of metal such as Ag, Sn, Cr or Ni are formed at both ends of the laminated body by this process. The dry process is selected for the purpose mainly of forming the external electrodes into thin films, thereby preventing the laminated body from being cracked or delaminated due to stress, etc. applied by the external electrodes.
In such a manufacturing method, when firing the laminated body, an oxide film may be formed or various contaminants may adhere onto surfaces of the internal electrodes which are exposed to surfaces of the laminated body. Further, internal electrodes may protrude or are depressed from the surfaces of the laminated body since the electrically conductive paste and the ceramic green sheets have different shrinkage coefficients.
Accordingly, an adhesion property is degraded between the external electrodes and the internal electrodes, thereby making the external electrodes liable to peel off. Further, the oxide film degrades electrical conductivity between the external electrodes and the internal electrodes. Furthermore, the external electrodes with thin film thickness have low step coverage and are liable to crack. Cracks allow moisture contained in atmosphere to penetrate into the electronic part, and lower its water resistance, reliability and so on.
The present invention has been achieved in view of the circumstances described above, and has a primary object to provide an electronic part with high precision, and is excellent in durability, water resistance and reliability as well as a manufacturing method thereof by enhancing an adhesion property between the internal electronic part and the external electronic part.
A second object of the present invention is to provide an electronic part which substantially prevents external electrodes from peeling off a main body of the electronic part, thereby being excellent in durability, water resistance and reliability as well as a manufacturing method thereof.
For accomplishing the primary object, the electronic part according to the present invention is configured as an electronic part including a laminated body which comprises electrically conductive internal electrode layers and ceramic insulator layers, and external electrodes composed of thin films which are formed by a dry process at predetermined locations of surfaces of said laminated body including locations where said internal electrodes are exposed and which are conductively connected to said internal electrode layers, and characterized in that at least said predetermined locations of the surface of said laminated body have a predetermined surface roughness.
This electronic part is capable of preventing the external electrodes from peeling off the laminated body owing to an anchor effect since the surfaces of the laminated body have the predetermined surface roughness. Further, the electronic part enhances a step coverage of the external electrodes.
In a preferable embodiment of the present invention, the step coverage is further enhanced by limiting a protruding height of the internal electrodes from the surface of the laminated body within a predetermined value. Similarly, the step coverage is enhanced by limiting a depression depth of the internal electrodes from the surface of the laminated body within a predetermined value.
Furthermore, the manufacturing method of the electronic part described above according to the present invention comprises forming (1) a laminated body including electrically conductive internal electrode layers and ceramic insulator layers by firing a laminated object composed of an electrically conductive paste and ceramic green sheets, and (2) external electrodes composed of thin films conductively connected to said internal electrodes at locations of surfaces of said laminated body including locations where said internal electrodes are exposed, and is characterized mainly in that the method comprises at least the predetermined locations of the surfaces of said laminated body are polished after the the laminated body is formed.
This manufacturing method of the electronic part makes it possible to prevent the external electrodes from peeling off the laminated body under an anchor effect since a predetermined surface roughness is obtained on the surfaces of the laminated body during the polishing step. Furthermore, the polishing step eliminates an oxide film and contaminant since surfaces of the internal electrodes, which are exposed on the surfaces of the laminated body are cut during the polishing. Accordingly, the manufacturing method enhances an adhesion property between the internal electrodes and the external electrodes.
In a preferable embodiment wherein a protruding height of said internal electrodes from the surfaces of said laminated body is limited within a predetermined value at the polishing step, a step coverage is further enhanced. The step coverage is further enhanced by limiting a depression depth of said internal electrodes from the surface of said laminated body within a predetermined value.
For accomplishing the primary object described above, the manufacturing method according to the present invention comprises a step to form a laminated body which comprises electrically conductive internal electrode layers and ceramic insulator layers by firing a laminated object composed of an electrically conductive paste and ceramic green sheets, and a step to form external electrodes composed of thin films which are conductively connected to said internal electrodes by a dry process at predetermined locations of surfaces of said laminated body including at least locations where said internal electrodes are exposed, and is characterized mainly in that the method comprises a step to form electrically conductive intermediate layers at least on the predetermined locations of the surfaces of said laminated body after the step to form said laminated body.
Owing to the intermediate layers, this manufacturing method enhances an adhesion property between the external electrodes and the laminated body even when the internal electrodes protrude or depress from the surfaces of the laminated body, and moderates stress applied by the external electrodes.
In a preferable embodiment of the present invention, the adhesion property between the internal electrodes and the external electrodes can be enhanced by configuring the intermediate layer formation step so as to comprise a step to apply a suspension containing a dispersed metal to the predetermined locations, a step to fuse the metal by heating the locations where the suspension is applied and a step to harden the metal by stopping the heating.
For accomplishing the primary object described above, the electronic part according to the present invention comprises a laminated body which comprises electrically conductive internal electrode layers and ceramic insulator layers, and external electrodes composed of thin films which are formed by a dry process at predetermined locations of surfaces of said laminated body including locations where said internal electrodes are exposed and which are conductively connected to said internal electrodes, and is characterized in that said external electrodes are made of a material which has a fusion point higher than that of said internal electrodes.
Further, the manufacturing method of the electronic part described above according to the present invention comprises a step to form a laminated body which comprises electrically inductive internal electrode layers and ceramic insulator layers by firing the laminated object composed of an electrically conductive paste and ceramic green sheets, and a step to form external electrodes composed of thin films conductively connected to said internal electrodes by a dry process at predetermined locations of the surfaces of said laminated body including at least locations where said internal electrodes are exposed, and is characterized in that said external electrodes are made of a material which has a fusion point higher than that of said internal electrodes.
This manufacturing method allows oxide films formed on surfaces of the internal electrodes to be decomposed since the surfaces of the internal electrodes which are exposed to the surfaces of the laminated body are fused at the step to form the external electrodes by the dry process. Accordingly, this method is capable of enhancing an adhesion property between the external electrodes and the internal electrodes.
For accomplishing the primary object, the electronic part according-to the present invention consists of a laminated body which comprises electrically conductive internal electrode layers and ceramic insulator layers, and external electrodes composed of thin films which are formed by a dry process at predetermined locations of surfaces of said laminated body including locations where said internal electrodes are exposed and which are conductively connected to said internal electrodes, and is characterized in said external electrodes are formed so as to have film thickness thicker than that of other locations at the locations where said internal electrodes are exposed.
A manufacturing method of the electronic part described above according to the present invention comprises a step to form a laminated body which comprises electrically conductive internal electrode layers and ceramic insulator layers by firing a laminated object composed of an electrically conductive paste and ceramic green sheets, and a step to form external electrodes composed of thin films conductively connected to said internal electrodes by a dry process at locations of surfaces of said laminated body including at least locations of the surface of said laminated body where said internal electrodes are exposed, and is characterized in that said external electrodes are formed so as to have film thickness thicker than that of other locations at the locations where said internal electrodes are exposed.
This manufacturing method enhances a step coverage of the external electrodes, thereby improving an adhesion property between the external electrodes and the internal electrodes even when the internal electrodes protrude from the surfaces of the laminated body by firing the laminated object.
In a preferable embodiment of the present invention, said external electrodes are formed by a dry process with a mask which has apertures formed at locations corresponding to the predetermined locations of the surfaces of the laminated body and film formation retarder members for reducing a film forming rate in the apertures. This method makes it possible to manufacture electronic parts, which have a high adhesion property between external electrodes and internal electrodes as described above.
For accomplishing the second object, the electronic part according to the present invention comprises a unit element which has nearly a rectangular parallelopiped form, and external electrodes which are formed at predetermined locations ranging from a first surface where said internal electrodes are exposed to second surfaces adjacent to said first surface, and is characterized mainly in that said external electrodes have film thickness which increases from ends of said external electrodes on said second surfaces toward said first surface, and a surface of the end of said external electrode on said second surface intersects with said second surface at an angle not larger than a predetermined angle.
The electronic part according to the present invention wherein the external electrodes have a film thickness on the second surface which is smaller than that on the first surface moderates a stress applied to the unit element at a stage to solder this electronic part onto a circuit board, thereby being capable of preventing the unit element from being cracked. Further, this electronic part is capable of preventing the external electrodes from peeling off the unit element since the external electrodes are configured so as to be thinner toward its ends on the second surface.
The manufacturing method of the electronic part described above according to the present invention comprises a step to form a unit element which comprises internal electrodes and has a nearly rectangular parallelopiped form, a step to form external electrodes at predetermined locations ranging from a first surface where said internal electrodes are exposed to second surfaces adjacent to said first surface of said unit element by irradiating with particles of a film forming material by a dry process, and is characterized mainly in that a film forming rate at said predetermined locations on said second surfaces is adjusted using a mask equipped with a film formation adjusting member which shadows portions of said predetermined locations of said second surfaces from the irradiation of the particles of said film forming material.
This manufacturing method deposits the film forming particles onto the second surface of the unit element while diffusing across the film formation adjusting members. Accordingly, the external electrodes are formed so as to have film thickness on the second surface, which is gradually increased from their ends. As a result, an electronic part manufactured by the method according to the present invention has a unit element which can hardly be cracked and external electrodes which can hardly peel off.
Other objects, configurations and effects of the present invention will be apparent from the following detailed description of the invention.